Archive for January, 2017

Metal Roofs – Aluminum vs Galvanized/Galvalume

Thursday, January 26th, 2017

All Metal Roofs Are Not Created Equal

The benefits of metal roofing in New England cannot be disputed. Although not all metal roofs are created equal, nor are they installed in the same manner. We are going to cover a vital item that is highly significant when it comes to residential applications. That is the base metal used for the roof.

Base metal, when used in the context of construction, is the primary component used in construction material, from the sheets of roofing exposed to the elements, right down to the fasteners contained beneath the roof. When used as part of a roof assembly, the base metals can be steel, aluminum, copper, or zinc, or a combination of base metals. All base metals have distinct properties which contribute to advantages and disadvantages in longevity and appearance when applied in various climate zones.

We will focus on two widely used base metals used in roofing: steel and aluminum. Steel is a hard, strong, gray or bluish-gray alloy of iron with carbon and usually other elements, used extensively as a structural and fabricating material. Aluminum is a silvery-white, soft, nonmagnetic, ductile metal. Both metals can be used for roofing. Steel can be used for structural roofing and architectural roofing. Aluminum is primarily used for architectural roofing. Architectural roofing does not require structural integrity in the construction assembly.

Galvanized and Galvalume Steel Roofing

It is important to note that base metals can be combined, coated, or layered with additional metals in a variety of bonding processes. Two popular roofing materials that use this process of binding two or more dissimilar metals are referred to as galvanized and galvalume, each of which use steel as the base metal. Iron or steel can be coated with zinc; this is known as a galvanized metal. The zinc acts as a protective layer to iron or steel to prevent rust. Galvalume is aluminum and zinc coated steel. The combination of aluminum and zinc is used once again as a protective layer to the steel. Steel exposed by itself without other protective metal coatings such as aluminum or zinc turns a reddish- or yellowish-brown flaky coating of iron oxide that is formed on iron or steel by oxidation, especially in the presence of moisture. It is what we refer to as “rust.”

Rust has been called “the great destroyer” and “the evil.” The Pentagon refers to it as “the pervasive menace.” It destroys cars, fells bridges, sinks ships, sparks house fires, and nearly brought down the Statue of Liberty. Rust costs America more than $400 billion per year—more than all other natural disasters combined. (reference: RUST: the longest war)

What Happens When the Protective Coating Wears Off?

Everyone has come across rust at some time in their life. We have all seen it before. Rust is unsightly. Shiny spokes on a bicycle wheel, or a dented corner panel on a car, all show the common enemy of rust becoming evident eventually. The question is would you want to see rust on your home’s roof in the future? Which base metal assures no rust whatsoever over the course of the roofs life? The only one of the three base metals we have looked at that is rust-proof is aluminum.

Metal working requires tools which bend, cut, and shape metal roofing components. Roof valleys and ridge caps are bent, roof edges are cut, and panels are formed and shaped depending on the particular style desired. All of this metal work by mechanics contributes to stresses on the metals and exposure of edges where a base metal may lose the protective coating, be it another metal or paint finish which is meant to keep it from rusting. This is particularly true for galvanized and galvalume roofs where the base metal steel is now exposed to the elements. Warranties for galvalume and galvanized roofing will call out a certain acceptable amount of rust from any edge that is cut within a specified period of time. Do you want to look up at a newly installed metal roof and wonder when the rust will show up, the paint finish will start peeling, and rust will begin running down your siding? I suspect not. So if that is true, you will want to choose to have an architectural aluminum roof installed, as aluminum does not rust. Aluminum, as you remember, is used to coat steel in the galvanized and galvalume products. You also do not want the fasteners holding your roof on, which may also be galvanized undergoing deterioration.

galvanic reaction on metal roof

The photo above shows galvanic reaction occurring, through the paint finish no less, of a steel based roof underneath the flashing of a drip edge above. This would not happen in a Kynar resin paint finished aluminum roof.

drip edge and rib bend in the galvalume standing seam roof

The photo above shows the drip edge and rib bend in the galvalume standing seam roof of the same home. If you examine the photograph closely, you will see the paint finish has chipped away underneath the drip edge where the steel base metal has begun to deteriorate (rust).

galvalume metal roof failure on commercial building

It is common for commercial buildings to use galvalume roofing as an initial cost saving measure. In the photo above we are beginning to see the failure of the paint finish along the seam of the bent metal. The failure is either in the paint resin, or the manufacturing process when the finish was adhered to the metal coil. Galvalume has a coating of aluminum over the steel and will likely take more time for rust to occur at the exposed locations of the panel. However, wear occurring along the roof’s drip edge where all the water and snow run off will eventually wear away the aluminum coating once the paint finish fails, and rust will ensue.

Only Aluminum Offers Long-Lasting Protection While Remaining Aesthetic

Paint finish warranties are key to understanding the expected longevity of a galvanized or galvalume metal roof. Aluminum roofing comes with paint finishes, as well, and have their own warranties. The big difference is that aluminum will oxidize/chalk if exposed to the elements, but the aluminum will not look unsightly and continue on with a rapid oxidation process (deterioration/rust), as steel will.

Be sure to visit Classic Metal Roofs website to see non-rusting roofs made with aluminum for your next architectural “metal” roof.

Written by Bryan Rusch, Partner at Classic Metal Roofs LLC. Additional articles related to metal roofing can be found on Bryan’s LinkedIn profile here:

Installing the Correct Underlayments for Your Metal Roof Project … “The Right Stuff”

Monday, January 9th, 2017

Selecting the right underlayments for a lifetime metal roof should be a primary concern for anyone thinking about specifying or choosing to install a metal roof on their home. The quality and type of underlayments used on the project in the long term will affect the overall performance of the roof.

metal roof underlayments image 1

Taking Care of Your Building Envelope

The roof is an important element of the Building Envelope. A Building Envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer. It needs to be addressed with the utmost care and consideration. Be sure that the contractor you choose is trained in the best methods of installation. Having the “Right Stuff” and not having the skill to do the installation nullifies the benefits of its use.

First Two Underlayment Layers

On most projects, there are two types of underlayments needed. The first on the list would be the ice and water shield. This is a roof membrane underlayment made up of either a rubberized-asphalt or butyl-based adhesive with a polyethylene carrier sheet. It has an adhesive backing with a peel and stick feature. This membrane should be labeled “high temperature” to withstand the surface temperature of the roof on a hot summer day. The heat in hot areas of the country, even here in New England, can exceed the melting point of some of these products. The product should be a premium, high temperature ice and water shield for use with tile, metal, and other roofs with scrim reinforced top surface. It self-seals around nails and provides protection for roof areas prone to ice and water intrusion.

The product needs to be installed on the eave edges up the roof at least two feet inside the face of any exterior wall. The rakes on gable roofs also need treatment to the same standard. All valleys and hips need to be covered. Penetrations such as chimneys, skylights, solar tubes, and vent pipes need to be surrounded with ice and water shield, as well.

If the roof slope is below 3/12 pitch (see our previous post on how to determine a roof’s pitch), the entire roof should be covered, but only if the roof is conventionally vented (cold roof construction).

Once the high temperature ice and water shield has been laid down, you can now add the second underlayment layer. This underlayment layer should be of the highest quality. If the roof is designed to last a lifetime, why would anyone want anything but the best? We recommend a polypropylene scrim reinforced underlayment made up of multiple layers. This type of underlayment is critical to a quality roof installation. It serves as a moisture barrier, as well as a slip sheet. Make sure the product is designed to be used under metal. Once again, this is used on cold roof construction.

When hot roof construction is done – a roof with no ventilation – a breathable underlayment is recommended. This allows moisture that can become trapped in the roof deck to evaporate and escape. This will prevent damage to the deck, stemming from rot and mold, over the long term life of the structure.

Third Underlayment Layer

There is a third product that is sometimes used and specified in new construction: That product is a mesh that would go on top of and over the other underlayment used. It is akin to cedar breather. It provides trapped moisture from under the roof in low slope applications a path to drain. It also creates a thermal break to minimize heat transfer from the roof surface to the structure. This thermal break promotes energy efficiency by stopping conductive heat transfer much like the air space between multiple panes of glass in a thermal pane window. This same break also provides sound attenuation by disrupting sound waves into the structure when rain hits the roof surface. The end result is a cooler, quieter, and healthier building. This product is generally used in hot roof low slope applications with aluminum roofing. See the image below.

metal roof underlayments image 2

To learn more about installing the correct underlayments for your metal roof project or to get a quote, feel free to contact us here.